This invention relates to integrated circuit and microelectromechanical systems (MEMS) devices. More particularly, this invention relates to a microfabricated optical apparatus wherein vias are formed completely through the silicon substrates.
Microelectromechanical systems (MEMS) are very small moveable structures made on a substrate using lithographic processing techniques, such as those used to manufacture semiconductor devices. MEMS devices may be moveable actuators, sensors, valves, pistons, or switches, for example, with characteristic dimensions of a few microns to hundreds of microns. One example of a MEMS device is a microfabricated cantilevered beam, which may be used to switch electrical signals. Because of its small size and fragile structure, the movable cantilever may be enclosed in a cavity to protect it and to allow its operation in an evacuated environment. Therefore, upon fabrication of the moveable structure on a wafer, (device wafer) the device wafer may be mated with a lid wafer, in which depressions have been formed to allow clearance for the structure and its movement. To maintain the vacuum over the lifetime of the device, a getter material may also be enclosed in the device cavity upon sealing the lid wafer against the device wafer. If a vacuum is not needed, the getter can be omitted and cavity can be filled with an inert gas such as Ar of N2.
One such device that may be manufactured using MEMS techniques is a microfabricated optical table. Microfabricated optical tables may include very small optical components which may be arranged on the surface of a substrate in a manner analogous to a macroscopic optical components mounted on a full sized optical bench. These microfabricated components may include light sources such as light emitting diodes (LED's), solid state lasers (SSL), beam shaping structures such as lenses and turning mirrors, and polarization altering devices such as Faraday rotators and optical isolators.
After fabrication, these devices may be enclosed with a lid wafer to protect them in an encapsulated device cavity. Some devices, such as infrared detectors and emitters, may require a vacuum or low moisture environment, such that the device cavity may need to be substantially hermetically sealed.
In order to control such a microfabricated elements, electrical access must be provided that allows power and signals to be transmitted to and from the elements. Previously, these signal lines were routed under the bond lines between the lid wafer and the device wafer. Because the enclosed elements may be delicate, the bondlines may be, for example, metal alloy bondlines that are activated at relatively low processing temperatures. However, the presence of the flat metal bondlines directly adjacent to potentially high frequency signal lines may cause unwanted capacitance in the structure, limiting its high speed performance.
Accordingly, encapsulated microfabricated high frequency optical structures have posed an unresolved problem.